Risk Assessment in the Nuclear Industry
PSA is today mandatory in most countries with nuclear power installations. The PSA typically include all phases of the life cycle from concept definition and pre-design through safe removal from operation. Most countries with nuclear power installations have regulatory authorities that require that all plants perform risk assessments to identify and quantify plant vulnerabilities in the design and operation.
In order to protect the environment from hazardous releases of radioactivity all nuclear installations must be designed, constructed and operated with a high level of technical safety. The defence in depth principle used in the nuclear industry means that multiple safety barriers, physical as well as administrative, are used in order to minimise the probability for core damage and release of radioactivity. Scandpower has a broad and deep experience within most areas with regard to reactor safety including development, revision and reviewing of documentation.
To be more specific, the basic aim of a Probabilistic Safety Assessment (PSA) is to identify combinations of failures that will cause all safety barriers of a nuclear power plant (NPP) to fail, leading to either severe core damage (PSA level 1), or to an unacceptable radioactive release to the environment (PSA level 2). Detailed analysis of land contamination and health effects resulting from a large release are done within a PSA level 3. The results of a PSA are expressed as frequencies (per year), and are dependent on the strength of the barriers. Thus, a PSA provides an integrated picture of the safety of a nuclear power plant (NPP), making it possible to identify weaknesses in design or procedures, and to assess, compare and prioritise among alternative safety enhancing measures.
The potential initiating events are sub-divided into internal events, area events and external events. Internal events are disturbances or accidents within the nuclear or thermal plant process, mainly transients and pipe breaks. Area events are events that occur externally to the process but within the plant, e.g., internal fire or flooding. External events occur outside the plant, e.g., aeroplane crash or effects from extreme weather (tornado, external flooding, extreme snow, etc.)